1. Field of the Invention
The invention relates to a method for detecting the type of replaceable piston-cylinder units for pipetting or dosing apparatus in which a piston of a piston-cylinder unit is connected with a piston rod, on the free end of which a piston rod head is positioned a code marking which may be sampled for determining the type of the inserted piston-cylinder unit, and in which the pipetting or dosing apparatus has a detection device for automatically identifying the piston-cylinder unit the piston-cylinder unit is inserted in the apparatus. The invention relates to a pipetting or dosing system as well as to a replaceable piston-cylinder unit for a pipetting or dosing system of the type used in the performance of such a method.
2. Description of Related Art
A method for detecting the type of a replacement part in the form of a respective piston-cylinder unit mounted on a pipetting apparatus is known from published European Patent Application EP 0 691 158 A2. For implementing the known method, a detection device is designed for identifying the type of the replaceable part with the help of its piston. Here, the piston has a code marking on its piston rod head, and the piston-cylinder unit is inserted into a receptacle of the pipetting device, so that the code marking is placed in a predetermined position relative to the detecting device. If the detecting device is formed, for example, as a photoelectric cell, identification of the type of the replaceable part is then carried out by evaluating the received light passages, or unsuccessful light passages at positions at which the code marking prevents such a passage of light.
This method requires observance of relatively high degrees of accuracy during manufacturing of the parts of the piston-cylinder unit, as the chain of tolerances piston rod head/piston rod/piston/cylinder bottom/cylinder flange is decisive for maintaining the exact relative position between the code marking and the detecting device.
A method for detecting the respective type of replaceable part mounted on a pipetting device in the form of a piston-cylinder unit is also known, wherein the influence of the chain of tolerances piston rod head/piston rod/piston/cylinder bottom/cylinder flange is eliminated. In this method (U.S. Pat. No. 5,389,341), the code marking is not mounted on the piston rod head, but on the cylinder flange. Such a code marking on the cylinder flange has drawbacks as explained in published European Patent Application EP 0 691 158 A2, column 1, line 42 to column 2, line 2.
The invention is thus based on the problem of designing and developing the known method for detecting the type of replaceable piston-cylinder units for pipetting or dosing apparatuses with the help of the code marking on the piston rod head, so as to eliminate the influence of the chain of tolerances piston rod head/piston rod/piston/cylinder bottom/cylinder flange so that, to a certain extent, larger tolerances may be tolerated for the parts of the piston-cylinder units.
A solution to the problem indicated above is obtained in acccordance with the method of the invention by generating relative movement between the piston rod head and the detection device and thereby detecting a reference point on the side of the piston head with the detection device, and by generating relative movement between the piston rod head and the detection device and thereby detecting a code marking of the piston rod head in order to determine the type of piston-cylinder unit mounted.
A solution to the problem indicated above is obtained in acccordance with the apparatus of the invention by relative movement between the piston rod head and the detection device being generated by means of a drive device, and during this movement, a reference point on the side of the piston head as well as the code marking are detected by means of the detection device, and the code marking is evaluated with respect to the reference point.
The objects of the invention also include providing a replaceable piston-cylinder-unit per se for use in a method according to the invention or in a device according to the invention.
In accordance with the method of the invention, the piston-cylinder unit is first inserted into the apparatus and the cylinder is mounted in the apparatus as usual. The piston rod head is coupled with the apparatus in an appropriate way during the insertion movement or subsequently. Next, detection of the presence of the piston-cylinder unit occurs first in order to be sure that such a unit is actually present in the apparatus. This detection may occur, for example, by actuation of an electric contact during the insertion movement.
According to a possible and advantageous course of the method, a reference point on the side of the piston rod head is detected. For this purpose, the piston rod head is moved past the detection device, which is fixedly positioned in the pipetting or dosing apparatus relative to the apparatus. Or else the detection device is moved past the stationary piston rod head. This detection of a reference point on the side of the piston rod head represents, as it were, a calibration for the subsequent detection of the type of inserted piston-cylinder unit, which makes the method according to the invention, at least to a large extent, independent of the differences in the dimensional tolerances of the parts. So by determining the reference point for each detection of type, it is possible to set an initial point for sampling the code marking of the piston rod head. Starting from the reference point, the detection device on the side of the apparatus is given a target, for example, from which instant of time or from which distance after detecting the reference point the detection of the code marking is to be expected or to be carried out.
In the next step of the method, based on the determined reference point, the code marking of the piston rod head is detected, with which the type of the inserted piston-cylinder unit may be determined. Moreover, a relative movement also occurs between the piston rod head and the detecting device. Because the reference point is detected on the piston rod head directly, it is possible to detect the code marking of the type of inserted piston-cylinder unit, practically regardless of tolerances. The tolerance is determined by dimensioning and tolerance in the manufacture of the piston rod head.
Detection of the reference point and of the type code marking may basically occur in any time sequence, therefore also simultaneously, according to the relative positions taken up by the reference point and the code marking, to how the code marking is formed, and to the applied evaluation method, normally an electronic evaluation method.
According to a more preferred embodiment, in a further step of the method, starting from the determination of the reference point, a marking code is determined in order to ascertain whether a piston-cylinder unit specific to the apparatus is present. Moreover, a relative movement between the piston rod head and the detecting device is also performed. If the code marking specific to the apparatus is detected in this step, then subsequent sampling of the code marking of the piston rod head is allowed to proceed, by means of which the type of inserted piston-cylinder unit is detected.
If, however, upon determining the first code marking, it is realized that a piston-cylinder unit not specific to the apparatus is present, the measurement is aborted and/or a relevant display on the apparatus is initiated, which signals to the user the presence of a piston-cylinder unit which is not specific to the apparatus. Then, for example, the relevant available type may be manually entered into the apparatus.
Otherwise, the piston-cylinder unit is removed from the apparatus and replaced with a piston-cylinder unit specific to the apparatus.
The term xe2x80x9cspecific to the apparatusxe2x80x9d means a piston-cylinder unit which comes from a certain manufacturer and is provided with a code marking which specifies the type, and which is detectable in accordance with the method of the invention.
Detection of the reference point, of the specificity to the apparatus and the code marking of the type may basically occur in any time sequence, and therefore, also simultaneously, as already stated above.
In a more preferred embodiment, the reference point may be detected by placing a thrust element on the side of the apparatus, on the piston rod head, preferably on its free face. Here, the piston may be pushed right down to its stop position in the cylinder with the help of the thrust element, in order to make sure that it is placed over the whole surface on the piston rod head. Dead space is thereby minimized in the piston-cylinder unit.
Preferably, the reference point may be detected by detecting a reference mark on the thrust element. This provides the advantage that the thrust element on the side of the apparatus represents a part which is unalterable at each detection, predeterminable as to its shape and size and, whereon the reference mark may be fixed with accurate positioning.
In a further more preferred embodiment, the sampling of the code marking of the piston rod head is carried out in dependence on the distance of motion of the piston rod head. Hence, for example, the magnitude of the distance covered by the piston rod head may be detected on the side of the apparatus and the code marking may be detected at the positions set earlier, and the type of the inserted piston-cylinder unit may be determined from the results of this detection.
The objects of the invention also include the provision of a pipetting or dosing system with an appropriate detection mechanism. According to an embodiment of the invention, the pipetting system or dosing system comprises a pipetting apparatus or a dosing apparatus which may, basically, be built as either a manually operable apparatus or a motor-driven apparatus.
Preferably, the apparatus is an autonomous, hand-held, motor-driven apparatus, which integrates all of the components in a casing. As usual, the components include a drive, preferably a motor drive, a geared device which transforms the rotational movement of the motor into a longitudinal movement of a piston drive, optionally, control electronics, a power supply and a coupling device for linking the piston of the piston-cylinder unit to the piston drive.
The piston-cylinder unit of the pipetting or dosing system according to the invention is formed as a replaceable part in which a sealed piston is movable for the purpose of sucking in and expelling a liquid to be pipetted or dosed. The piston comprises a piston rod on the free end of which a piston rod head is mounted. The piston rod head bears a code marking which specifies the type of the piston-cylinder unit.
Additionally, the pipetting or dosing system according to the invention comprises a detection device for automatically detecting the type of a piston-cylinder unit mounted on the apparatus.
Furthermore, the pipetting or dosing system comprises a drive device which generates a relative movement between the piston rod head and the detection device, wherein a reference point on the side of the piston head and the code marking are detected during this movement by the detection device. Preferably, the drive device of the piston rod head moves past the detection device. However, the detection device may also be moved while the piston rod head stays still.
Preferably, the drive device produces both the movement of the piston rod head and the relative movement. Alternatively, two drive devices may be provided, in particular, when it is desired to move the detection device for detecting the reference point and the code marking in the apparatus.
Normally, in a pipetting or dosing apparatus, a measuring device is available for determining the relative distance covered between the piston rod head and the detection device, or between the piston rod head and the apparatus. This is also advantageous in the pipetting or dosing system according to the invention, so that the distance for the relative movement may also be detected.
Preferably, a photoelectric cell is provided as a detection device. In the simplest case, the photoelectric cell may comprise an infrared diode as a light source on one side, and an infrared detector facing it on the other side of the apparatus, so that the piston rod head, during its movement relative to the detection device, moves right through between these two elements. This provides the advantage that several code markings may be sampled with a single photoelectric cell. Also, the code marking is not bound to a fixed grid.
However, in order to accelerate the detection process, the detection device may also comprise two or more pairs of photoelectric cells (one photodiode as a light source and one photodetector as a receiver, respectively) placed at a distance from one another along the path of motion of the piston rod head in the apparatus.
Furthermore, the pipetting or dosing apparatus is provided with all the required electronics and all the data processing units which are required for carrying out and evaluating the detection of the type of the mounted piston-cylinder unit.
A replaceable piston-cylinder unit for a pipetting or dosing system according to the invention or for application in a method according to the invention is an independently marketable part.
In the following, the invention will be explained in detail with reference to a drawing illustrating only exemplary embodiments. The description of the exemplary embodiments illustrated in the drawing does not limit the extent of protection, which is defined by the patent claims.